It is not known when An Lushan's son An Renzhi was born, although he was said to be not yet twenty when Emperor Xuanzong gave him the mostly honorary title of minister of vassal affairs, likely in 751.

He is An Lushan's second son, and his mother is An Lushan's first wife Lady Kang.

At some point, Emperor Xuanzong had given him the name of Qingxu.

The first definitive historical references to him were in 752, when, in a defeat that An Lushan suffered against the Xi, An Lushan was said to have fallen into a hole and was only saved through the effort of An Qingxu and others.

Also that year, when An Lushan's close associate Ji Wen went to meet An Lushan before departing for the Tang capital Chang'an, it was An Qingxu that An Lushan sent to accompany Ji to the borders of his territory.

When An Lushan rebelled at his post at Fanyang Circuit (headquartered in modern Beijing) in 755, An Qingxu was apparently with his father and accompanied his father south.

In response to An Lushan's rebellion, An Qingxu's mother Lady Kang and older brother An Qingzong, then at Chang'an, were executed, and after An Lushan captures Chenliu Prefecture (roughly modern Kaifeng, Henan), it is An Qingxu who realizes that An Qingzong had been executed and who tearfully informs his father, sending his father into a rage in which he executes the Tang soldiers who had surrendered to him at Chenliu.